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Psittacosaurid Individual and Taphonomic Variation

From: Ben Creisler

New in PLoS ONE:

Brandon P. Hedrick & Peter Dodson (2013)
Lujiatun Psittacosaurids: Understanding Individual and Taphonomic
Variation Using 3D Geometric Morphometrics.
PLoS ONE 8(8): e69265.

Psittacosaurus is one of the most abundant and speciose genera in the
Dinosauria, with fifteen named species. The genus is geographically
and temporally widespread with large sample sizes of several of the
nominal species allowing detailed analysis of intra- and interspecific
variation. We present a reanalysis of three separate, coeval species
within the Psittacosauridae; P. lujiatunensis, P. major, and
Hongshanosaurus houi from the Lujiatun beds of the Yixian Formation,
northeastern China, using three-dimensional geometric morphometrics on
a sample set of thirty skulls in combination with a reevaluation of
the proposed character states for each species. Using these
complementary methods, we show that individual and taphonomic
variation are the joint causes of a large range of variation among the
skulls when they are plotted in a morphospace. Our results demonstrate
that there is only one species of Psittacosaurus within the Lujiatun
beds and that the three nominal species represent different
taphomorphotypes of P. lujiatunensis. The wide range of geometric
morphometric variation in a single species of Psittacosaurus implies
that the range of variation found in other dinosaurian groups may also
be related to taphonomic distortion rather than interspecific
variation. As the morphospace is driven primarily by variation
resulting from taphonomic distortion, this study demonstrates that the
geometric morphometric approach can only be used with great caution to
delineate interspecific variation in Psittacosaurus and likely other
dinosaur groups without a complementary evaluation of character
states. This study presents the first application of 3D geometric
morphometrics to the dinosaurian morphospace and the first attempt to
quantify taphonomic variation in dinosaur skulls.